As the energy and environment issues become increasingly urgent, higher requirements are imposed on emission control of automobile exhaust, so as to protect the environment and save energy. In China, National V Emission Standard of Natural Gas Engines is issued on Jan. 1, 2013. China has abundant natural gas, and natural gas as fuel is widely used in both buses and taxis in many cities. Also, as sustainable energy, natural gas will be applied to automobile fuels in future. Therefore, it is imperative to strengthen the research on post-treatment technology for emission control of natural gas vehicles, and as a key part of the post-treatment technology, catalysts are particularly important. As compared to gasoline vehicles, the exhaust catalyst technology for natural gas vehicles is still in the initial stage of development and is not technically mature enough.
Zhao Bin et al. (Journal of the Chinese Society of Rare Earths, Article ID: 1000-4343(2003)-0098-03) prepares a natural gas purification catalyst by using La—Al2O3, La—Al2O3+CeO2—ZrO2 and La—Al2O3+CeO2—ZrO2·MnOx as support materials and adding the support materials together with additives and noble metals during the ball-milling slurry-making process. According to this invention, the noble metals are liable to migrate from the inside to the coating surface, which leads to the reduction of noble metal concentration from the surface to the inside, over-accumulation of noble metals on the surface, and high loss rate, and finally causes poor catalyst performance.
Chinese patent (CN200810225539.1) prepares a catalyst by performing ball-milling on catalytic materials to a certain particle size, impregnating with noble metals, oven-drying and calcining to make powders, then performing ball-milling to make a slurry, applying the slurry to a ceramic honeycomb support, oven-drying and calcining. This method has the advantage that the noble metals are supported on a fixed material before milling, which prevents the noble metals from migrating during slurry milling According to this invention, the noble metals are dispersed on the powder surface before milling, the powders are destroyed and broken to form new sections during slurry milling; however, these new sections do not have noble metals to implement catalysis effect, resulting in low catalyst performance.